	CS 580 Client-Server Spring Semester, 2004 Networks
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References
Dr. Vinge's CS580 class notes, Spring 2000, http://www-rohan.sdsu.edu/faculty/vinge/courses/spring00/cs580/

Unix Network Programming by W. Richard Stevens, 1990, selected pages

Internetworking with TCP/IP Volume 1 Principles, Protocols, and Architecture, Third Edition, by Douglas E. Comer, selected pages

Computer Networks and Internets, Comer, 1997


Doc 13, Networks Slide # 2

Networks

Communication Network

A set of communication nodes that are interconnected to permit the exchange of information


Doc 13, Networks Slide # 3

How information is transmitted in a network

Information is transformed into electrical or optical signals

All signals are corrupted during transmission

Transmission adds noise to the signal

Digital data helps over come noise


Slightly corrupted 1's are distinguishable from slightly corrupted 0's
Digital data allows for error-control

Dynamic data like audio or video normally requires continuous transmission


Doc 13, Networks Slide # 4

Packets
Stream of bits is divided into separate packets

Kermit Packet Structure


Doc 13, Networks Slide # 5

Classes of Communication Services

End-to-end services as seen by the users:

Synchronous communications

Bit stream is delivered with a fixed delay and given error rate
Each bit reaches the destination with the same time delay after leaving the source

Asynchronous communications

Bit stream is divided into packets
Packets are received with varying delays, so packets can arrive out of order
Some packets are not received correctly
Connection-oriented

Packets are delivered in order
System confirms delivery and put packets in order
Error free

Connectionless

Packets are treated individually
Program has to worry about order, error and lost packets
Expedited Data Faster delivery than normal


Doc 13, Networks Slide # 6

Our View of Network Communication with TCP/IP

TCP - Connection-oriented

UDP - Connectionless

TCP gives us a "pipe" between machines to allow us to send messages between machines

UDP
Fast

Client & Server must handle

Lost packets
Packets arriving out of order

Used by:

Games
NFS


Doc 13, Networks Slide # 7

TCP
Handles

Lost packets
Packet order

Receiver acknowledges each packet

Sender resends packet if it is lost

TCP has delays in

Startup of connection
Closing of connection


Doc 13, Networks Slide # 8

Addresses and Names
IP address is currently a 32-bit number

   130.191.3.100      (Four 8 bit numbers)

IPv6 uses 128 bit numbers for addresses

   105.220.136.100.0.0.0.0.0.0.18.128.140.10.255.255
   69DC:8864:0:0:0:1280:8C0A:FFFF
   69DC:8864::1280:8C0A:FFFF

Machines on a network need a unique IP address


Doc 13, Networks Slide # 9

127.0.0.1 (localhost)
Common loopback address

Refers to the current computer

Messages sent to 127.0.0.1 to not reach the network


Doc 13, Networks Slide # 10

Domain Name System (DNS)
Maps machine names to IP addresses

rohan.sdsu.edu <-> 130.191.143.100

Unix "host" command

Shows mapping between machine names and IP address

->host rohan.sdsu.edu
rohan.sdsu.edu has address 130.191.3.100
   
->host 130.191.3.100
100.3.191.130.IN-ADDR.ARPA domain name pointer rohan.sdsu.edu


Doc 13, Networks Slide # 11

Top Level DomainsCurrent TLD

Domain Names	Meaning
COM	Commercial organizations
EDU	Educational institutions
GOV	Government institutions
MIL	Military groups
NET	Major network support groups
ORG	Organizations not list above
ARPA	obsolete
INT	International organizations
CN,IN,MX,US	http://www.iana.org/domain-names.htm
biz	Business
info	Information
name	For individuals
pro	For professionals
aero	Forviation
coop	For coopertives
museum	For museums

More top level domains will be added later this year
Dealing for applications is March 15, 2004 at 23.59 UTC

Internet Corporation for Assigned Names and Numbers (ICANN http://www.icann.org/) oversees assigning TLDs


Doc 13, Networks Slide # 12

Ports

TCP/IP supports multiple logical communication channels called ports

Ports are numbered from 0 - 65535

A connection between two machines is uniquely defined by:

Protocol (TCP or UDP)
IP address of local machine
Port number used on the local machine
IP address of remote machine
Port number used on the remote machine

Well known ports	1 - 1023
Registered Ports	1024 - 49151
Dynamic/Private ports	49152 - 65535


Doc 13, Networks Slide # 13

Some Interesting Server Port Numbers

Service	Port Number
echo	7
discard	9
daytime	13
character generation	19
ftp	21
ssh	22
telnet	23
smtp	25
time	37
http	80
nntp	119
https	443
doom	666
mysql	3306
postgresql	5432
gnutella	6346, 6347

For a local list of services
file://rohan.sdsu.edu/etc/services
For a complete list see:

See IANA numbers page http://www.iana.org/numbers.html for more information about protocol numbers and assignment services


Doc 13, Networks Slide # 14

Telnet is Your Friend
Telnet & port 23

A server is running on port 23 on rohan
The server asks you log in

Telnet Client and other ports

Can send ASCII to a server


Doc 13, Networks Slide # 15

Examples to Try
Day Time
Type:

telnet   sdsu.edu    13

Course Web Site
Type

telnet www.eli.sdsu.edu 80


then type:

GET  /courses/spring04/cs580/index.html   HTTP/1.0 <CR>
<CR>

Note <Cr> indicates were you need to hit return

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